A lot of research is nowadays going on in the pipeline to develop designer drugs or therapeutics based on genes after the completion of the human DNA sequence of entire human genomes. Explorations into drug design and gene therapies have need of gene tests for individual patients. The gene tests take considerable times, for example several days for current technology. To cope with this, it remains a major challenge to develop analyzers very small in construction called μ TAS short for Micro Total Analysis System or Lab-on-a chip. The μ TAS refers to a microscopic system in which laboratory functions including chemical reaction, metering, pumping, and so on are all integrated on a single chip to make it possible to conduct desired analysis procedure with a less time than ever known. With the microscopic analyzing system constructed as stated earlier, all components necessary for the chemical analysis are mounted on a single chip to shrink in construction the whole system itself, saving reaction time to ultimately cut the times desired for testing.
Among the conventional micropumps are the construction using the one-way valve to allow fluid flow only in one direction, the turbo-type construction like the spiral pump having the rotary part such as rotor. There is further other construction having sophisticated geometry. As being easily imaginable from fluid mechanics, any force dominating the behavior of fluids changes with others depending on whether there is on microscale phase or microscale phase. In microscale flow, the surface force including viscous force and frictional force is predominant over the body force including inertia force and so on. This causes any damage to moving parts and turning components combined in the micropump, raising a major issue of having the micropump itself short-lived. Moreover, the micropump with mechanical components of intricate configuration results in increasing the number of the parts desired, which would give rise to the questions of several more chores to produce many parts and members with precision and assemble them together. Meanwhile, the micropumps are known in which the diffuser/nozzle elements different in configuration are used. Most diffuser/nozzle elements, after review of them, have been turned out to be made in any one of steeply divergent and convergent configurations lying midway between a fluid channel and a pumping chamber. With the micropumps relying on the differential resistance in the fluid channel, it has already been found that the channel geometry combining together the diffuser/nozzle elements constructed as stated earlier is worse in efficiency for the reason their mutual effects get cancelled each other out in relation with the variation in flowing direction of the oscillatory fluid.
One of the prior micropumps is disclosed in for example patent document 1 enumerated later in which there is provided at least one pair of blocks raised in a pressure chamber or a fluid channel communicating with the pressure chamber in a geometry lying in a plane parallel with a diaphragm surface. The micropump is comprised of a first substrate of silicon wafer having a diaphragm actuated to make in part vibration, and a second substrate of silicon wafer combined together with the first substrate in very close contact, the second substrate having the pressure chamber in opposition to the diaphragm. The pressure chamber communicates on one side thereof with a nozzle having shrunk increasingly in width as getting closer the pressure chamber and on other side thereof with another nozzle also having shrunk increasingly in width as getting farther from the pressure chamber. The blocks are raised in pairs at locations where the nozzles are most restricted in width in a relation extending in parallel with the center lines of the nozzles. With the constructed as stated earlier, the blocks are made in geometry their projected images on the plane parallel with the diaphragm surface conform to extension lying on inside wall surfaces of the nozzles.
Moreover, the patent document 2 listed later discloses a micropump befitted to transfer a minute quantity of fluid selectively in either of forward and reverse directions even though made simple in construction. The prior micropump is composed of a first channel whose flow resistance varies depending on the differential pressure, a second channel in which the rate of variation in flow resistance in response to the differential pressure changes is less than in the first channel, a pressure chamber interposed between the first and second channels to communicate them each other, and a piezoelectric element actuated to have the pressure chamber deformed to change the internal pressure thereof. Energization of the piezoelectric element causes the variation in the pressure inside the pressure chamber to change a ratio between the flow resistances of the first and second channels. Changes in the flow resistances relative to the differential pressure changes have the fluids squeezing selectively either of forward and reverse directions.
Another micropump is known in, for example the patent document 3 listed later in which an outlet check valve is made on a substrate surface of intermediate substrate of silicon wafer to cover a fluid outlet hole. The prior micropump, more particular, includes a glass substrate made with the fluid outlet hole and recessed partially below a surface to be joined together with other substrate in close contact, the intermediate substrate of silicon wafer having a fluid inlet and outlet holes to allow the fluid running through there, and another substrate of silicon wafer having a mesa-structure and a diaphragm. All the substrates are stacked one on top of the other in very close contact and sealed hermetically. The outlet check valve is placed on one substrate surface of intermediate substrate of silicon wafer to cover the fluid outlet hole, while an actuator is arranged underneath the diaphragm to drive the diaphragm to open and close the check valve.
The fourth patent document 4 listed later disclosed a vane-type micropump having a housing and a rotor enclosed inside the housing. The rotor includes a rotor body mounted off-center, vanes free to move radially of the rotor body and leaf springs to connect the vanes to the rotor body to urge the vanes outwardly, these parts being all combined integrally into a unitary construction.
The patent documents 1 to 4 stated earlier refer to the following material information.
Patent document 1: Japanese Patent Laid-Open No. H10-110681
Patent document 2: Japanese Patent Laid-Open No. 2005-98304
Patent document 3: Japanese Patent Laid-Open No. H11-257233
Patent document 4: Japanese Patent Laid-Open No. 2004-11514